NORTH CHARLESTON, S.C. –  The hull of the first submarine in history to sink an enemy warship has been cleaned and revealed for the first time in 150 years.

After a year of painstaking work, scientists using small chisels and hand tools have removed encrusted sand, sediment and rust from the outside of the hand-cranked Confederate submarine H.L. Hunley.

Now, the outside appears much as it did when the Hunley and its eight-man crew rammed a spar with a powder charge into the USS Housatonic and sank the Union blockade ship off South Carolina in 1864.

But scientists said Thursday that cleaning the hull didn't solve the mystery of why the Hunley itself sank with its crew before returning from its mission.

NO SMOKING GUN...

Cleaning the hull showed some dents on both sides of the submarine. But scientists say it's not clear when the dents occurred. The Hunley sank twice before it went on its 1864 mission, though it also could have been dented at the time of the Housatonic attack or later when the sub sat for decades on the ocean floor off Charleston. "If there was a smoking gun, we would have seen it a long time ago," said Johanna Rivera-Diaz, a conservator with the Hunley project.

...BUT MORE CLUES

The most significant find from cleaning the hull is an indication that a wooden boom at the front of the Hunley that supported the spar with the powder charge was damaged in the attack. It appeared as if the boom had been pushed back into the sub. That would be consistent with the boom striking a vessel, said Michael Scafuri, an archaeologist with the project.

A LOT OF WORK

The conservation team has laboriously removed about 1,200 pounds of sediment and other gunk from the outside hull of the Hunley, which was built in an attempt to break the Union blockade that was strangling Charleston. That's roughly the same weight as a grand piano.

THE NEXT STEP

The next step in conserving the submarine, which was discovered in 1995 and brought to a conservation lab in North Charleston 15 years ago, is to remove encrusted sediment from the inside. That process will take another year, said Kellen Correia, president and executive director of Friends of the Hunley. The work will take time because conservators will work in the cramped 4-foot diameter interior of the sub.

INSIDE CLUES?

Scafuri said that cleaning the inside of the Hunley is vital to understanding how it worked and perhaps why it sank. "We have to learn how it functioned and how it was intended to function and then we can take the next step and see if anything went wrong," he said. "We're basically looking at the cabin. This is where the guys were and where they were operating."